Sprayfoam or Specialty Coatings for Interiors

Spray foam

My 50 ft steel displacement river boat is completely spray foamed on the inside of the hull above the waterline (about 2.5 inches thick). The painted inside of the hull was cleaned to be fat free and then sprayed between the frames and under the coach roof and deck.

The excess foam was cut with an electrical heated wire absolutely plane with the frames. The whole area covered with foam, was then covered with aluminum foil (vapor barrier). Wooden laths about 2 inch wide and 1 inch thick were srewed onto the T-frames and the complete interior mounted on this laths. By this method, free circulation of air is possible behind the interior. In combination with double glased windows, the boat is insulated to its optimum and I never had any problems with humidity in the boat.

The only problem with this method, you can only apply it to smaller boats. Commercial vessels and classed yachts are not allowed to be insulated with foam because foam is not fire retardend according to Class. For bigger boats you need to use mineral rock wool with vapor barrier.

Because I have no plans to have an open fire in my boat, I am very happy with this type of thermal insulation .

An interesting read on mineral wool:

Modern House Plans by Gregory La Vardera Architect: What you don't know about Mineral Wool will make you look stupid.